Microphonic material and method of producing the same



Nov. 24, 1931. FRUTH 1,833,640

MIGROPHONIC MATERIAL AND METHOD OF PRODUCING THE SAME Filed Dec. 51.1928 //7 yen/0r 7 H0/ f/h/f/z Patented Nov. 24, 1931 UNITED STATESPATENT OFFICE HAL FBEDERIGK PRU TH, OF CHICAGO, ILLINOIS, ASSIGNOR 'IOWESTERN ELEUIRIG COMPANY, INCORPORATED, 015 NEW YORK, N. Y., A.CORPORATION OF NEW YORK This inventibn relates to microphonic materialand methods of producing the same,

and more particularly to a coated, variable resistance material for usein microphone or telephone transmitters.

Objects of the invention are to provide an improved microphonic materialand meth' d of producing the same to provide a microphonic material ofsuperior elasticity and sensitivity; to provide a microphonic materialhaving a high melting point and good wearing properties; and to providea relatively light microphonic material which shall be capable ofcarrying a heavy electric current.

In general terms, the present invention contemplates the use as amicrophonic material of particles of an elastic substance such as glassor other vitreous substance, each particle being coated with a thinlayer of metal or other conducting substance, such as platinum oriridium. The invention further contemplates an improved method for"producing the microphonic material wherein a very thin layer of metalis applied to particles of glass or other elastic substance by acathodic sputtering method. In a microphonic material composed of suchparticles, the layers of metal or other conducting material are incontact with each other to permit electrical current to passtherethrough, and when pressure is applied to the material, as by atransmitter diaphragm, the particles of glass or other elastic materialare distorted in such a manner that the electrical resistance of thematerial is decreased, but when the pressure is released the particlesresume their normal positions quickly because of the high'elasticity ofthe material. The particles are preferably of spherical, spheroidal, orhollow spherical shape, although granular material may also be used.

The invention will bemore fully understood from the followingdescription, taken in connection with the appended drawings, in whichFig. 1 diagrammatically illustrates an apparatus for coating theparticles, and

Fig. 2 is a greatly enlarged sectional view of one form of particlewhich may be used to make up the microphonic material.

MICROPHONIG MATERIAL AND METHOD OF PRODUCING- THE SAME Application filedDecember 31, 1928. Serial No. 329,645.

In the drawings, which are to be construed her by means of a rod 17 ofinsulating material and is connected to anode 14 by means of anelectrical circuit 18 which includes the secondary of a transformer 19;The cathode is preferably provided with a cover or shield 20 Within thevacuum chamber is positioned a frame 22 which supports a bin 23containing a supply 24 of the particles to be coated.

vBy means of a gate 25 the particles are allowed to roll by gravity overan inclined platform 26 which is paralled to and immediate- 1y below thecathode 16, the particles forming a continuous layer 27 which ispreferably not more than one particle deep at any point. In order toprovide for slow but continuous movement of the particles over theinclined platform, a cylinder 28 is mounted at the lower edge of theplatform and is driven at a slow speed by a coiled spring 30 connectedthereto by suitable gears 31, 32 and 33. A governor 35 is connected tothe train of gears by spiral gearing 36 and 37. A receptacle 38 ispositioned to receive the particles passing over cylinder 28.

A vacuum of .1 of mercury or thereabouts is maintained in the vacuumchamber by means of the vacuum pump connected to tube 12, the degree ofevacuation being regulated by means of a manually operated bleeder valve40, the pressure being indicated by a gauge 41.

It will be understood that when a suitable vacuum is produced in thechamber and transformer 19 is energized, current will flow therefrom tocathode 16 and thence through the exhausted atmosphere to anode 14 inthe known manner, carrying with it particles of the metal forming thecathode 16 and depositing such particles upon any objects which may liein .their path, thus coating the layer of particles 27 by the processcommonly known as cathodic sputtering. In order to prevent reversal ofthis action, the surface area of cathode 16 is made several timesgreatously during their passage, thereby presentspheroidal ing theirentire surfaces to the stream of metallic particles and acquiring a thinuniform coating. I

Fig. 2 shows a spherical bead 43 of glass or other vitreous substancehaving a coating 44: of metal thereon. Such beads without the coating)may be readily made by a process of liquid comminuting and solidifying.The beads may vary considerably in size, and since both the larger andthe smaller sizes are undesirable in microphonic material they should begraded by sifting. A satisfactory material may be obtained by thusselecting only those beads which pass a 50-mesh screen and are rejectedby a 100-mesh screen, althou h the size of the beads may be varied widey depending upon the particular nature of the instrument in which thematerial is to be used and upon other factors.

Hollow beads of the sizes and shapes above specified may be used inplace of the solid beads illustrated in Fig. 2. It is also within thescope of the present invention to use as the basis of the microphonicmaterial beads formed of metallic oxides, also granular particles suchas may be obtained by crushing and sifting quartz, glass, or othercrystalline or vitreous material, the essential qualities of suchmaterial being hardness, elasticity, and lightness.

Microphonic material formed in accordance with this invention has a highelasticity and sensitivity, a high melting point and good wearingproperties.

It is obvious that the method and apparatus shown and described hereinmay be widely varied without departing from the spirit of the inventionas defined in the following claims.

What is claimed is:

1. Microphonic material consisting of metal-coated glass beads.

2. Microphonic material consisting of hollow, metal-coated glass beads.

3. Microphonic material consisting of particles of glassTcoated withplatinum.

4. Microphonic material consisting of particles of glass coated with anoble metal.

5. Microphonic material consisting of partlcles of insulating materialhaving a coating of metal deposited thereon by cathodic sputtering.

6. Microphonic material consisting of particles of a non-carbonaceousmaterial having a coating of metal deposited thereon by cathodicsputterin 7. Microphonic material consisting of particles of an elasticmaterial having a coating of conducting material deposited thereon bycathodic sputtering.

8. Microphonic material consisting of particles-of glass coated with anoble metal by a cathodic sputtering process.

9. A method of producing microphonic material which consists in coatingparticles .of an elastic substance with metal by cathodic sputtering.

10. A method of producing microphonic material which consists incathodically sputtering on glass-particles a coating of noble metal.

.11. A method of producing microphonic material which consists insuccessively moving vitreous particles adjacent a metallic cathode, anddepositing on said particles a coating of metal by sputtering from saidcathode.

12. A method of producing microphonic material which consists insuccessively rolling glass particles adjacent a metallic cathode, andactivating the cathode to cause metal to be transferred therefrom to theparticles.

13. A method of producing microphonic material which consists inpositioning particles of insulating materialv adjacent a metalliccathode for a predetermined period, and activating the cathode to causemetal to be transferred therefrom to the particles.

14. Microphonic material comprising particles of glass coated withconducting material.

In witness whereof, I hereunto subscribe my name this 19th dayofDecember, A. D.,

HAL FREDERICK FRUTH.

